The present invention relates to an imaging method, particularly for use in oil-filled passages such as wells of pipelines, or for passages containing other similar viscous fluids.
Imaging sensors are well-known devices which comprise an optical system, a detector and electronics to provide at a remote point a representation of the image seen by the sensor. An imaging sensor forms the heart of a video camera system which is used in wells or pipelines to provide, outside the hole or pipe, e.g. on a screen or monitor, a visual image of the situation at a point of interest in the hole or pipe.
Early systems for surveying wells used mechanical arrangements for photographing the inside of a well and for providing television images of the inside of the well. Such systems are disclosed, for example, in U.S. Pat. No. 2,632,801; U.S. Pat. No. 2,852,600 and U.S. Pat. No. 2,912,495.
It has been realised that the presence of oil may adversely affect the imaging system.
With imaging sensors operating in the visible light wavelength, problems arise because often the fluid medium in which the system is required to operate exhibits little transmission of visible light and/or contains particles or bubbles which cause significant scattering of visible light. Various attempts have been made to overcome the problems caused by oil, etc. inside the wells.
For example, U.S. Pat. No. 2,912,495 discloses a system wherein oil is cleaned from the lens by hydraulic purging.
WO 94/28440 attempts to deal with this problem by providing a chemical surfactant to the surface of the lens to prevent oil, etc. adhering to the lens and thus to prevent a remote viewing camera from being obscured by oil and other such fluids.
An article entitled xe2x80x9cFiber Optics Improve Downhole Videoxe2x80x9d by Philip K. Schultz and Charles Cobb in the Oil and Gas Journal of May 11, 1992, page 46ff. describes the development of downhole imaging systems. In this article, the problem of oil or other opaque fluids adversely affecting the image obtained is discussed. Generally, as discussed in this article, the opaque fluid has to be displaced and this is most commonly done by pumping filtered brine or other transparent mediums, e.g. nitrogen.
The problem of oil or other viscous fluids obscuring the view of the camera is also discussed in an article entitled xe2x80x9cWell Preparationxe2x80x94Essential to Successful Video Loggingxe2x80x9d by J. L. Whittaker and G. D. Linville in SPE 35680.
The problem is also identified by EP-A-0264511 which discloses use of an arrangement of photosensitive elements in an annular array, together with a system of reflecting elements to obtain a high resolution undistorted view of the inner wall of a cavity.
Other systems use particular lighting arrangements in an attempt to improve the image obtained. Some such systems are disclosed, for example, in U.S. Pat. No. 5,402,615 and U.S. Pat. No. 5,663,758.
EP-A-0643198 discloses a video logging system having a remote power source. In this system, the problem of oil, mud, etc. reducing the quality of the image obtained is dealt with by using high intensity lamps.
WO 91/19884 discloses a video logging system also having a remote power source and using optical fibres to conduct the camera signals to the surface for remote viewing.
All of the above systems, whilst identifying the fact that the down-hole images are obscured by oil, mud, etc. all attempt to deal with this problem by using additional mechanical means or higher power lamps, etc. This all increases the cost, complexity and weight of the imaging system.
The aim of the present invention is to overcome the problems identified above and to enable clear images to be provided to a remote point outside of the well, without the need for additional complex and expensive apparatus.
Accordingly, the present invention provides a method of providing images of the interior of a cavity filled with a fluid opaque to visible light, comprising transmitting and detecting infrared or near infrared radiation through the fluid inside the cavity and providing an image at a remote point according to the detected radiation.
In a preferred embodiment, the present invention uses a downhole imaging sensor comprising illuminating means, optical transmission means and optical detector means operating in the infrared wavelength region, and further comprising circuitry to perform image processing, based on the signals detected by the optical detector means. The image processing circuitry preferably compresses the received signals and transmits them to a remote plane.
The illuminating means, the optical transmission and detector means and the electronic circuitry are preferably all arranged in a protective housing for protection from the operating environment.
The inventor has discovered that because the sensor operates in this preferably infrared wavelength region, it can capture an image of the scene despite the presence of oil or other fluids which do not transmit sufficient visible light to form a useful image.
The sensor may be provided with means for controlling its movement and position inside the pipe or well. Various means may be used, e.g. a slick wireline, an electric wireline or a fibre-optic wireline. Also, or alternatively the sensor may be attached to a tractor.
Similar means may also be provided to allow power, and/or control information to be transmitted to the sensor, and/or to transmit image and status information from the sensor.
The image processing circuitry may carry out various processing functions to derive useful information from the sensor signals. For example, the processor may determine the volumes of bubbles of different fluids in the surrounding medium and the velocities of those bubble from successive images. The processor may also calculate the flow rates of different fluids in the surrounding medium and record and/or report or display the information.
The image processing circuitry may also locate scattering particles in the surrounding medium by comparing successive image frames and distinguishing the particles by their velocity relative to the sensor. These particles can then be removed from the image.